You got it. The 4th constant is a little tricky. You have to calculate it! Using your old original sketches to read time, measure how far off it is from the PC time today, and again in 10 days. Let's say it's 45 seconds slower than it was today. Divide by the number of days (10), then multiply by 100. The answer is 450. That's what you put for spdx100. That stands for Secs/day x 100 that it is slow. -450 if it's faster after 10 days running. Let me know! The error seems consistent to me, so now there is much less error per day.